Method and apparatus for wet grit blasting



March 31, 1953 N. RANSOHOFF 2,632,980

METHOD AND APPARATUS FOR WET GRIT BLASTING Filed July 8. 1949 6 Sheets-Sheet '1 M I INVE-NTOR. 16??! BY 411mm? vs March 31, 1953 N. RANSOHOFF 2,632,930

METHOD AND APPARATUS FOR WET GRIT BLASTING Filed July 8. 1949- 6 Sheets-Sheet? v Q INVENTOR. 0? I Ra V L! V' w 1 I 47707 514 75.

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March 31, 1953 RANSOHOFF 2,632,980

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ATToR/VFYSI March 31, 1953 N. RANSOHOFF 2,632,980

METHOD AND APPARATUS FOR WET GRIT BLASTING Filed July 8. 1949 6 Sheets-Sheet 5 V INVENTOR.-

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METHOD AND APPARATUS FOR WET GRIT BLASTING Filed July 8. 1949 6 Sheets-Sheet 6 g I 5 I INVENTOR.

Patented Mar. 31, 1953 METHOD AND APPARATUS FOR WET GRIT BLASTING Nathan Ransohoff, Cincinnati, Ohio, assignor to N. Ransohoif, Incorporated, Cincinnati, Ohio, a

corporation of Ohio Application July 8, 1949, Serial No. 103,703

12 Claims.

This invention relates to the art of surface treating work pieces by the projection of abrasive particles at high velocity. This technique is known generally as grit blasing and is employed for the purpose of improving surface texture or quality, and particularly for the purpose of removing surface scale or adherent dirt or particles as in the treatment of rough sand castings and the like.

In conventional grit blasting methods, the abrasive particles, either sand, metal fragments or metal shot are propelled at high velocity upon the work surfaces by means of a blast of air, or by means of a so-called slinger which projects the particles through its own speed of rotation. The operation of grit blasting is a dusty one. Particles of the abrasive impacted on the surface of the work piece loosen dirt or scale either by attrition or by dislodgement and dust is liberated which pervades the atmosphere adjacent the work surface. The operation usually is conducted in the chamber of a grit blasting machine which is provided with a suitable exhaust system, but even so, the liberation of dust is a nuisance and, when the dust is of silicious nature, the operator is exposed to the dangers of contracting silicosis.

One of the principal objectives of this invention has been to provide grit blasting apparatus and improvements in the art of grit blasting by which dust formation is suppressed. More specifically, this invention contemplates a wet grit blast technique in which impaction and attrition of the abrasive particles upon the Work occurs under wet conditions to such extent that any fine particles which normally would appear as airborne dust are dampened and thereby held against escape into the atmosphere.

Some grit blast machines have been built for the projection of a liquid slurry or suspension of abrasive upon work but in each instance of this sort, the abrasive particles are exceedingly fine, as for example, from 60 to 1200 mesh, the slurry being aspirated from a source of supply through an air blast nozzle. Such abrasive slurries are useful in the treatment of work surfaces to improve the surface texture or to remove light oxide films but the particles of such slurries are much too fine foruse in the grit blasting of coarse castings or the like where removal of a substantial quantity of adherent sand or surface particles must be accomplished in a short period of time or where there is to be a material alteration of the work surface. The use of metallic grit of high specific gravity and large particle size in such 2 methods has been totally impossible; for example, grit particles or fragments up to A; inch in average diameter are much too heavy and dense, to be aspirated through a nozzle in an air blast or liquid stream and, of course, such particles cannot be pumped by ordinary methods.

This invention is predicated upon the concept and determination of establishing a dynamic suspension of grit blast particles of substantial size by forming a mixture of grit particles and liquid and advancing such a mixture at a low rate of velocity which is sufliciently high to keep the particles in a state of apparent suspension. Thus, the term, dynamic suspension, as used in this specification and throughout the claims is intended to designate a condition of distribution of grit particles in liqud which will be maintained while the liquid is in movement. Next, this stream moving at low velocity and keeping its particles in a state of suspension in so doing, is advanced to a projector which is effective for accelerating the velocity of the stream and the particles contained within it,up to the speed required for grit blasting. Otherwise expressed, the invention in one respect is predicated upon the discovery that, while it is not possible to pump a liquid containing large particles of grit at grit blasting speed because of the attrition of the particles upon any conduit through'which they must pass, still it is possible and practical to deliver a mixture of grit and water or liquid in an appropriate state of suspension of the particles up to the point of projection at a low velocity and then to impart additional energy to the particles which is requisite for them to accomplish the grit blastlng function. This procedure eliminates the abrasion or wear which would otherwise be involved and enables all of the advantages and eliciency of a dry grit blast system to be obtained without the nuisance of dust. Furthermore, it is found that by conducting the blasting in the presence of liquid, a finer surface finish is produced.

To form the suspension, or more particularly, to advance a dynamic suspension of the particles or liquid, a pump somewhat akin to a centrifugal pump with provisions for introducing liquid and grit into it simultaneously has been found suitable. Such a pump, operated to advance the mixture at a, low rate sufilcient to dynamically suspend the particles, does not suffer excessive year. From this point, the stream is advanced to a projector where the final high velocity is imparted to it. The projector either may be in the form of an air blast nozzle or in the form of a slinger wheel and both embodiments by way of illustration are shown in the accompanying drawing. Following projection of the stream upon the work surfaces, which is conducted in a chamber on account of splashing, the grit and the dislodged dirt fall and the water drains to a sump. The grit, of course, falls almost immediately to the bottom while the water is allowed to accumulate in a layer above it. The layer of grit at the bottom constitutes a supply awaiting recycling to the low velocity pump. Meanwhile, however, it has been dis-covered that a substantial portion of the dirt dislodged from the work, in typical grit blasting operations, is sufficiently light in density as to form at least a temporary suspension in the water over the grit.

In common production operations, a system of the type just described would soon become overcharged with accumulated dirt since, in typical operations, the amount. of dirt removed, for example as sand from a rough casting, is appreciable. However, an important feature of this invention is predicated on the concept of discharging a portion of the water accumulated over the grit into a settling or separatory apparatus where the suspended dirt is removed, as by common settling, from the water or liquid so as to leave the liquid in a relatively clean condition adapted to be recycled back to the machine. Thus, the clean suspension system and the dirt removal system may be in communication with one another through the chamber or the sump of the chamber in which blasting is conducted, with the dirt separation system functioning to condition the water for reuse. The advantage of this arrangement reside in the fact that the liquid portion of the treatment media is not subjected to dilution through constant additions of make-up liquid to it. Hence, the concentration of any added chemical such as a rust inhibitor or the like is not diluted.

In one embodiment, the invention incorporates a throwing wheel or slinger mounted on a resilient structure, which permits the wheel to rotate at blasting speed without transmitting vibrations to the apparatus. The grit particles are discharged by a nozzle into the interior of the wheel which has radial vanes, the grit particles being intercepted by the leading edges of the vanes which travel substantially at the same rate as the particles, whereby the grit particles are accelerated uniformly as they are propelled outwardly by the vanes toward the periphery of the wheel. The work pieces are conveyed upon a rotary table relative to the blasting wheel so that the pieces are treated by advancing them through the grit blast stream. In this instance, there is provided also a flushing station which projects jets of the settled or clarified liquid upon the work surface after treatment, to remove the foreign materials dislodged by the blast stream. The sump, which is disposed beneath the table, is arranged to contain a mass of grit particles and water, preferably containing a rust inhibiting solution, to protect the cleaned work surfaces. Grit particles and liquid thus fall by gravity from the work table to the sump for recirculation. In this form of apparatus, the Work pieces are treated in batches for a time period as determined by the particular class of work, each piece of work being passed successively through the blast stream at a proper speed to obtain the desired result.

The apparatus is adapted for utilization in well known commercial machines such as rotary tumbling mills, either the batch or continuous type, and also machines of the class incorporating a conveyor arranged to advance the work pieces through a treatment tunnel. As applied to rotary machines, one or more blasting wheels or other suitable projectors may be installed upon shafts extended into the tumbler so as to project grit streams upon the work pieces as they are agitated in the rotating tumbler or the wheel may beset to impel the grit into the open end of a tilted barrel. In conveyor type machines, one or more grit blasting wheels may be installed within the tunnel in positions to project the grit streams against opposite sides of the work pieces as they are advanced past the wheels by the conveyor. Also, work may be treated by placing it in fixed position in the blast stream for a timed, treatment period or by moving the projector relative to stationary work pieces.

From the foregoing disclosure of the principles involved, and from the detailed description taken in conjunction with the drawings, those skilled in the art will comprehend readily the various modifications of which the invention is capable.

In the drawings:

Figure 1 is a general front elevation of a grit blasting machine embodying the present improvements.

Figure 2 is a side elevation of the machine further illustrating the general arrangement of parts.

Figure 3 is a sectional view taken on line 3-3 of Figure 2, illustrating generally the internal structure of the machine.

Figure 4 is a horizontal sectional view taken on line 44 of Figure 3, illustrating the mounting arrangement for the grit blasting wheel with respect to the treatment chamber and the driving apparatus for the wheel.

Figure 5 is an enlarged fragmentary sectional view taken from Figure 3, detailing the relationship of the grit conveyor and the grit pump.

Figure 6 is a sectional view taken on line 6-6 ofFigure 5, further detailing the construction of the grit pump.

Figure 7 is a fragmentary sectional view taken on line 1-1 of Figure 4, further detailing the yieldable mounting for the grit blasting wheel and its relationship with the work support table.

Figure 8 is an enlarged sectional view taken on line 8-8 of Figure 4, detailing the construction of the grit blasting wheel.

Figure 9 is a sectional view taken on line 9-9 of Figure 8, further illustrating the grit blasting wheel and the relationship of the grit supply nozzle with the wheel.

Figure 10 is an enlarged end view of a grit blasting wheel generally similar to that illustrated in Figure 8. the wheel being equipped with a modified form of a grit supply nozzle.

Figure 11 is a sectional view taken on line Il-H of Figure 10, further illustrating the modified grit supply nozzle associated with the wheel.

Figure 12 is a view generally similar to Figure '7, with an air operated grit blasting nozzle substituted for the grit blasting wheel.

Figure 13 is an enlarged sectional view detailing the. construction of the blast nozzle shown in Figure 12.

The apparatus disclosed in the drawings represents one organization by which the invention may be practiced and constitutes a treating machine having a rotary table arranged to 'convey work pieces successively through a grit blast stream and a rinsing station where the work pieces are flushed with a liquid solution, preferably water, containing a rust inhibitor. The grit and liquid are stored ina sump beneath the work table and in a settling tank respectively and recirculated continuously by a grit pump to the grit wheel and by a liquidpump to the spray pipe.

The grit particles preferably consist of metallic particles such as steel or metal shot, having a density substantially greater than water and greater than non-metallic grit. These particles settle quickly to the bottom of the sump to be conveyed mechanically to the grit pump, whereas the scale and dirt form a sludge of lesser density which remains in suspension at least temporarily in the water.

Since it is necessary to flush the work pieces with relatively clean water after grit blasting, the sludge is removed by drawing the liquid from the upper portion of the sump and passing it through a settling apparatus for removing the sludge before conducting the liquid to the spray pipe. Thus, one supply of liquid is drawn directly from the sump to provide a carrier for the grit particles, While another portion is drawn from the sump and clarified before being recirculated to the rinsing station.

Described with particular reference to Figure 3 of the drawings, the apparatus in general consists of a treatment chamber l5 having a rotary work support table [6, a grit blasting wheel l1 arranged to propel a blast stream of grit particles upon the work pieces carried by the table, and a spray pipe I8 arranged to flush the work pieces with jets of water or liquid solution after the grit blast treatment.

As above noted, the same solution preferably is used as a carrier for the grit particles and for the flushing treatment, there being provided a sump [9 in the base of the chamber for receiving the liquid and grit after passage over the work. The grit, which is considerably more dense than the liquid, settles almost immediately to the bottom of the sump after blasting to be recirculated to the blasting wheel. For

this purpose there is provided a screw conveyor the blasting wheel and a second system, indie cated at 23, arranged to draw off liquid from the upper portion of the hopper and to discharge the liquid into a settling apparatus for sludge removal, subsequently to be recirculated back to the spray pipe. 'The settling apparatus 24 is disclosed in the present instance as a pair of decanting tanks, although it is intended in connection with larger machines, to provide a sludge and sand removal apparatus having a mechanical conveyor passing through a settling tank for continuous operation.

In the present disclosure, the chamber i5 may be formed from sheet metal in the form of a square or rectangular housing having a, pair of converging side walls -25;-25, forming. the hopper or sump l9 which is generally v -shaped as viewed in Figure 2. conveyor trough 26 in. which is rotatably mounted the conveyor screw 20, arranged to feed the grit particles to the grit pump 21 loa liquid passes with the grit into the pump, and an additional supply of liquid is drawn from the upper level of the sump and, discharged into the bottom of the pump to prevent any accumulation of grit in the pump bottom.

At the front of the housing, there is provided a door 30 for loading and unloading the work table and for general utility in operating and servicing the machine (Figures 1, 2 and 4): The door is supported at its upper end by a pair of inclined lugs 3l-3l welded or otherwise secured to the chamber adjacent the door opening (not shown); The door includes a pair of studs 32-32 secured upon its upper edge and projecting outwardly from opposite sides and resting upon the lugs. The lower edge of the door is confined by a vertical flange 33 secured to the housing beneath the door opening and spaced from the housing so as to slidably conline the edge of the door between the flange and housing. In closed position, the lower edge of the door is held against the housing by the flange 33 and the upper edge by the inclined lugs 3|. The door includes a handle 35 by which it may be lifted out of engagement with the lugs and flange and either removed entirely or swung to an open position for access into the chamber. Along the opposite sides of the door opening, there is mounted a pair of brackets 36-36 angularly related to the housing and designed to maintain the door in an inclined position in front of the door opening with the lower edge of the door resting against the housing; During operation of the machine, the door is kept closed to prevent grit particles from being discharged from the machine, although for observation purposes, the machine may be operated with the door partially open, as above noted As shown, the machine is supported by vertical legs 31 formed preferably from angle irons, the upper ends of the legs being welded or otherwise secured to the chamber as at 38. The lower ends of the legs are connected to a framework 39 whichbraces the legs and provides'a support for the driving mechanism of the grit conveyor as hereinafter disclosed.

Grit conveying apparatus As illustrated in Figure 3, the sump l9 provides a common reservoir for a supply of grit particles indicated at 40 and the liquid, preferably consisting of water, indicated at 41, including a rust inhibitor compound. In operation, a continuous supply of grit is advanced by the conveyorto the grit pump 2! and, at the same'time, a'supply of liquid is drawn from the sump by conduit 42 and introduced into the bottom of the pump casing at the center thereof (Figure 2). The grit particles are fed intothe center of the pump impeller The side walls form a from above'by the..conveyor,' as illustrated in Figure .5. By operation of the impeller, the grit particles are intermingled with the liquid and discharged into the flexible conduit'43 which leads to the grit blasting wheel or slinger H3. The mixture is conducted through the conduit at a velocity sufficient to maintain the particles in dynamic suspension, but insumcient to perform the blasting operation or to cause substantial Wear upon the pump or conduit. The upper'end of the conduit 43 passes through the housing and is con nected to the blasting wheel nozzle in the manner shown in Figure 4 or alternately, to the air blast nozzle as shown in Figures 12 and 13.

Described in detail, the grit conveyor constitutes a spiral vane or screw which includes a shaft 44 having its opposite ends journalled in bearings 45 and 45. The shaft extends through the upper bearing c and includes a sprocket 41 for driving the screw. Since bearing is below the liquid level in the sump, it is provided with-a packing gland to prevent leakage of liquid. The packing glandand bearing is a commercial product and, for this reason, is not disclosed in detail, The lower bearing 46 is mounted upon the top of the pump casing within the wel1 28, submerged in the liquid. Both bearings are provided with suitable seals to protect the bearing surfaces against the entry of grit particles and sand.

The driving apparatus for the conveyor screw preferably is a commercial variable speed unit mounted upon a base plate 48 supported by the legs 3'! and framework 39 beneath the sump (Figures l, 2 and 3). The unit, in general, consists of a motor 50 having a variable diameter V-belt pulley 5| of conventional construction. The motor pulley 5| is connected by a V-belt52 to a V-belt pulley 53 mounted on the shaft of a speed reducer unit 5 1. On the opposite end of the speed reducer, there is provided a sprocket 55 which is connected to the conveyor sprocket 4'! by a chain 56. Conveyor speed is regulated by shifting the motor relative to the speed reducer unit. For this purpose, the motor is mounted upon an adjustable base 51 having a hand wheel 58 arranged to shift the motor relative to the speed reducer and thus to change the effective diameter of the motor pulley. By virtue of the variable speed unit, the rate of grit feed to the blast wheel may be regulated according to the particular requirements of the operation.

The lower or discharge end of the conveyor screw feeds the grit in the presence of the liquid maintained above the pump, directly into the grit pump through an opening 59 formed by a collar 60 mounted in the top wall of the pump casing (Figures 5 and 6). Since the conveyor screw is provided with a single spiral vane 6|, it will be evident that the discharge of grit will be intermittent, that is to say, there will be a concentrated discharge each time the trailing end of the vane makes one revolution through the lower zone of the conveyor trough. In order to provide a continuous discharge, a device is provided which regulates the flow of grit particles by restricting the passage of material from the conveyor to the grit pump.

This device consists of a collar 62 welded or otherwise secured in the end wall 63 of the hopper and provided with a stationary control disk 54 secured within the collar and operating in conjunction with a disk 65 secured to and rotatable with the screw shaft 44. As shown in Figures 3 and 5, the'rotary disk 65 includes blades 66 which are pitched in the same direction as the screw vane 8 6'|'.'whi'le:thei blades 6130f the-stationary disk are pitched in the opposite direction. The rotary blades 66 preferably have a collective pitch equal to one turn of the screw vane andthe stationary blades have an equal pitch in the opposite direction. It is found that this arrangement effectively regulates the discharge of grit without building up back pressure against the conveyor screw.

Grit pump The grit pump, consists of a circular casing 68 having a rotor or impeller generally indicated at 69, enclosed within the casing by end plate assemblies ii] and 1| (Figures 5 and 6). The casin 68 includes upper and lower circumferential flanges '|2'|2 The end plate assemblies are secured by means of bolts 13 passing through matching apertures located at spaced intervals around the circumference of the pump. The inner ends of the bolts are provided with nuts and washers Hi and I5. Eachgof the end plate assemblies l0 and H consist of a pair of metal plates '|6'|6 having a sheet 11 of rubber, synthetic rubber or the like interposed in compression between the plates.

The impeller consists of a pair of disks 18-18 spaced apart from one another and having a series of spiral vanes 18 interposed between the spaced plates and secured by welding. Above and below the respective plates, there is provided secondary sets of spiral vanes and 8| which supplement the pumping action of the vanes 19. It will be noted that the collar 6!] extends through a central opening formed in the top disk 18 of the impellerso that the material discharged from the conveyor passes through the collar directly into the pumping zone between the impeller disks for actuation by the inner or leading edges 82 of the vanes '59. As shown in Fi ure 6, the inner edges of vanes 19 and Bil'terminate at the outside diameter .of collar 60 while the inner ends 83 of the secondary vanes 8| extend inwardly to the hub 84 which is welded as at 85 to the lower impeller disk.

Liquid is introduced through the bottom of the pump through a pipe 86 connected to the flexible tube or hose 42, the opposite end of which communicates with the hopper at a point above the level of the grit mass but below the liquid level. The liquid flows into the pump casing and is impelled radially ,by operation of the lower vanes 8| to prevent accumulation of grit particles at the bottom of the pump. The mixture of grit and liquid introduced through the opening 59 also flows radially from between the impeller disks so that the grit particles are picked up by the moving stream of solution at the bottom of the casing and intermingled with it for discharge into the pump outlet 87. Outlet 81 constitutes a section'of pipe generally tangent to the pump impeller, the pipe being welded to an opening formed in casing 68. The casing includes a partition 88 at one side of the opening to complete the passageway from the pump casing to the outlet. The mixture of grit and liquid is conducted by the flexible conduit 43 from the outlet 81 upwardly to the grit blasting wheel as hereinafter disclosed. Pipe 86 preferably includes a fitting 89 including axvalve 90 for draining the liquid from the sump.

The previously noted pump well 28 is in the form of a cylindrical shell formed of sheet metal and having its vertical edges 9| secured by welding to the end wall of the hopper. This structure provides a mounting for the pump, the upper plate I8 of the pump being secured to the lower edge of the shell by welding as at 92 (Figure 5).

The pump is driven by means of a vertical shaft 93 journalled in bearings 94-94 secured to the end wall of the chamber and driven by a motor 95 mounted near the top of the chamber (Figures 1, 2 and 3). Upon the upper end of the shaft 93 there is provided a V-belt pulley 96 connected by belts 91 to a V-belt pulley 98 mounted on the motor shaft. The lower end of the pump drive shaft passes downwardly through the well 28 and has its lower end keyed to the hub 84 of the pump impeller.

The grit impeller is detachably secured to the shaft 93 by a screw 99 passing through a segment I which is welded as at IOI to the inside diameter of the hub 84 (Figures 5 and 6). The segment fits into a notch I02 cut into the end of the shaft so as to key with the segment and provide a driving connection between the hub and shaft. The segment is formed most conveniently by cutting it from the end of the shaft so as to form the notch I02 in the shaft corresponding in shape to the segment. The segment then is welded into the hub as shown and is drilled to provide a hole for the screw 99, which is threaded into the shaft, preferably with the parts in assembly.

Grit blasting wheel The mixture of liquid and grit from the grit pump is conducted by the tube 43 to discharge tained by driving the wheel at a speed of approximately 4,000 B... P. M. Since the grit velocity is determined by the peripheral speed of the wheel, it will be apparent that a smaller diameter of wheel necessarily is driven at a greater speed than a larger one. The speed also is determined by the grit size and the class of work being cleaned.

By reason of velocity, there is a pronounced I tendency for the wheel to setup vibrations which ordinarily are transmitted to the entire machine, causing noisy operation and undue wear on the wheel bearings. This condition is substantially eliminated by resiliently mounting the wheel and nozzle assembly with respect to the chamber. For this purpose, there is provided a spring mounted frame I04 disposed in a horizontal plane above the work table, the frame providing a bearing for supporting the wheel and also a mount for the grit nozzle ,fixed relationship and in axial alignment with the I05, the nozzle being mounted in wheel center. By this arrangement, the wheel floats relative to the blasting chamber so that upon reaching a settling speed,it is free to rotate about a center which may be slightly eccentric to its true center. The arrangement eliminatesthe necessity of accurately balancing the wheel. Since the discharge nozzle is fixed upon the sameframe 04, vibration of the wheel does not alter the relationship between the nozzle and Wheel.

The frame I0 3 is made up preferably of angle iron sections I06 suitably joined together to provide a rigid structure. The nozzle I05 is mounted by means of a pillow block I01 bolted as at I08 to the frame, the nozzle being adjustably secured with respect to the pillow block by means of a set screw-I09 passing through block E01. The dischargeend of the nozzle is curved as at IIO approximately at right anglesto the body of the nozzle. By this arrangement, the grit is projected directly into the inner or leading edges of the vanes of the grit blasting wheel and as hereinafter disclosed, the angle of discharge from the wheel can be regulated by rotary adjustment of the nozzle. I

As shown in Figure 9, the grit blasting wheel consists of a pair of rotor disks III and H2 spaced from each other and provided with a series of spiral vanes 12 is joined to the disks preferably by welding. Disk III includes a hub II4 by means of which the wheel assembly is mounted upon theend of a drive shaft H5. The Wheel is detachably secured by means of the screw H6 passing through a segment II? and screwthreaded into the end of the shaft, the segment fitting into a notch Ila to key the Wheel to the shaft. This arrangement is similar to that disclosed in connection with the grit pump and the circular segment, in this case also, may be formed by cutting it from the end of the shaft in the manner previously noted. shaft [I5 is journalled in a bearing IE9 secured by screws I20 to the frame structure on the side opposite to the nozzle. The shaft extends through the end wall of the chamber and is journalled in a bearing I2I secured to the wall. Bearings H9 and I2I preferably are ball bearings of commercial design, the bearing I2I being of the type which permits angular shaft motion, whereby the wheel assembly is free to vibrate without injury to the bearing. The respective bearings are protected by stuffing boxes or slinger rings I22I22, one being secured to the inner surface of the chamber wall, the other being mounted upon a rail 23 spanning the frame I04. The stufling boxes may be of any design suitable to prevent the entry of grit particles into the bearings.

The frame IE4 is yieldably mounted by the spring units I20 connected to the respective corners of the frame, the opposite ends of the spring units being anchored upon angle irons I25 and I26 located on opposite sides of the frame. I The inner mounting angle iron I25 is mounted within the chamber with its ends secured preferably by welding to the walls of the chamber. The other angle iron I26 is secured upon the outside surface of the chamber wall, also by welding. Each tension unit constitutes a link I27 having one end pivotally connected to the corner of the frame by a screw I28 and having its opposite end connected to a plunger I29 by a pivot pin I 30. A spring I3I is disposed under compression upon the plunger, one end of the spring being seated against a rubber grommet I32 seated against the vertical web I33 of the angle iron I25. The 0pposite end of the spring restsagainst a washer I3 8 engaged by a nut I35 screwed upon the end of plunger I29. By means of these nuts the tension of the respective units is adjusted and equalized with respect to one another to align the wheel assembly properly with respect .to the bearing I2I. By exerting tension in opposite directiqns, the frameis maintained in) tangent to the wheel.

"aes aeep tension in a level plane and by virtue of the springs and pivotal action of the links I27, the wheel assembly is free to vibrate in vertical and horizontal planes and thereby prevent the transmission of vibration and noise to the machine and to permit the wheel to find its natural center of rotation.

As shown in Figures 3, 4 and '7, there is provided a semi-circular shroud or grit shield I35 extending over the upper circumference of the blasting wheel. The lower ends of the shroud include a pair of angular extensions or feet I31, formed by bending the ends outwardly. The feet are secured by means of bolts I38 passing through the angle irons I04. The purpose of the shield is to prevent stray grit particles from being projected against the top and side walls of the chamber; also to prevent the particles from being projected towards the door opening with possible injury to the operator should the door be left open.

The vanes I3 of the grit blasting wheel are spirally arranged between the disks III and H2, the edges of the vanes being secured to the respective disks by welding. As above disclosed, disk III is secured tothe drive shaft H and provides a mounting plate for the wheel while disk IIZ includes an opening I40 for entry of the discharge nozzle I65. As shown in Figure '7, the leading edges I4I of vanes H3 are disposed closely adjacent the opening l ili in a position to intercept the stream of grit and liquid discharged from the nozzle I05.

The initial discharge velocity of the stream is substantially the same as the velocity of the leading vane edges I4I so as to reduce the impact of the particles against the leading edges and thus prevent excessive vane wear. By virtue of the configuration of the vanes, the grit particles are accelerated at a fairly uniform rate as the particles slide from the leading edges toward the trailing edges at the circumference of the wheel by centrifugal action. By regulating the angle of the discharge nozzle I65, the discharge path of the blast stream can be regulated with respect to the work table so as to cause the particles to strike the proper portion of the table. As indicated in Figure '7, in broken lines, the path of the particles generally is fan shaped and The angle of the stream is determined by the velocity of the wheel in conjunction with the angle of the discharge nozzle. The driven speed of the wheel necessarily is regulated by the size of the grit particles and the class of work being blasted. In setting up the machine, it is necessary to adjust the angle of the nozzle according to these factors in order to achieve maximum efficiency.

The wheel is driven by any acceptable means, for example by a motor indicated at I42 (Figures 1 and 2). The wheel is connected to the motor by a pulley I43 keyed upon the outer end of shaft H5 and driven by a V-belt I54 passing over a pulley I45 mounted on the shaft of the motor. The rate of grit feed to the blasting wheel, as previously noted, is controlled by adjustment of the variable speed unit so that operating characteristics can be governed accurately.

Work support table During the grit blasting operation, the work table I6, which is circular, is rotated by a friction pulley I46, engaged against the circumference of the table by a lever I41 which is pivotally mounted as at I48 between a pair of angle irons I55I56 mounted within the chamber (Figures 3 and 4). The lever urges the pulley toward the table under the influence of a spring I5I having one end hooked upon the outer end of the lever as at I52 and having its opposite end anchored upon the chamber wall as at I53. The lever I 11 is U-shaped as viewed in Figure 3, having limbs I54 I54 with the pulley disposed between the limbs and driven by a shaft I55. The pulley is'keyed to the shaft and the shaft journalled in the limbs I54--I54.

' Shaft I55 rises vertically to a speed reducing unit I56 mounted on the top of the chamber. In

F order to permit angular movements of the pulley I46, a universal joint I51 is interposed in the shaft. The speed reducer I56 is driven from the grit pump shaft 93 by means of a V-belt I58 passing over pulley 56 of the pump shaft and extending to a standard type of variable speed idler pulley I59, adjustably mounted upon the top of the chamber to regulate the speed of the table. The speed reducer I56 is driven by a second V- belt I60 passing over the variable idler pulley I59 and pulley I6I of the speed reducer. The table thus is rotated by the same motor which drives the grit pump.

The table is rotatably mounted by a shaft I62 journalled in a pair of spaced bearings I63--I63. Bearings I63 are mounted upon a frame I64 constituting spaced angle irons I65I65 secured Within and extending crosswise of the chamber. A strap I66 extending crosswise between the angle irons supports the upper bearing and the lower bearing is supported by a hanger structure I5! extending downwardly from the angle irons.

In operation, the grit particles and liquid impinge upon the work pieces, then drop to the hopper for recirculation, For this purpose, the table includes suitable apertures (not shown) and there is provided also beneath the table a screen I68 spaced above the hopper to prevent castings, which may be dislodged from the table, from dropping into the hopper. The screen is of a mesh which is sufficiently coarse to permit the grit particles to pass without interference.

A slightly modified grit nozzle arrangement is illustrated in Figures 10 and 11. As shown, the nozzle IIil is located generally at a tangent with respect to the direction of wheel rotation as viewed endwise (Figure 10). In order to introduce the discharge end of the tube into the blasting wheel, the nozzle is extended angularly into the opening I46 of disk H2 instead of being in axial alignment with shaft II5 as illustrated in Figure 11.

The discharge end III of the nozzle in this instance is formed by cutting the end of the nozzle at an angle which is related chordwise to the radius described by the leading edges of the vanes (Figure 10). One advantage of this arrangement is that the grit particles travel more nearly in a straight line through the nozzle to the leading edges of the vanes as distinguished from the change in direction caused by the curved nozzle I55. The stream is intercepted by the leading edges of'the vanes and is accelerated uniformly by reason of the increasing peripheral speed as the grit particles advance toward the trailing edges of the vanes.

The nozzle I70 is adjustable with respect to the axis of the blasting wheel in the manner previously disclosed, by the pillow block I01, and set screw I09. In order to sustain the nozzle body at an angle and at the same time to permit 13 the nozzle to be adjusted radially, the nozzle is supported by an arm I12 welded or otherwise secured to a shaft I13, passing through the bearing block I01 in place of the nozzle I05. By rotating the shaft, which is on the same axis as shaft I I5 of the wheel, the discharge end I1I swings in an arc concentric with the radius described by the leading edges of the vanes to control the discharge angle of the grit blast stream.

Liquid spray system In operating the apparatus, the work pieces are treated for a predetermined time period according to the class of work, type of material and other determining factors. Each treatment is a continuous one, the work pieces passing through the blast stream for treatment after which the pieces sequentially pass beneath a spray pipe for exposure to jets of liquid to remove the sand, sludge and other materials dislodged by the grit treatment. The spray treatment also removes from the work pieces any particles of grit which may adhere. The liquid then drains to the sump for recirculation. As previously noted, the liquid contains a rust inhibitor of a type conventionally used in cleaning metal parts.

Described in detail, the spray pipe indicated at I14 in Figures 3 and 4 extends radially across the table at the forward section of the chamber and is provided with a series of apertures to project the liquid in jets upon the pieces carried by the table. The liquid is supplied to the spray pipe by the recirculating system 23 previously noted, The liquid flows from the sump by gravity through the pipe I15 opening into the chamber near the liquid level in the sump. The liquid in the sump is substantially free of grit particles but contains sand, scale and sludge which has been dislodgedfrom the castings. Since the flushing is performed most efliciently with a clear solution, the liquid drawn off from the sump passes through the separator for removal of the solids before recirculation. The separator disclosed is in the form of decanting tanks I16 and I11 although it is contemplated in connection with larger equipment to provide a mechanical separator, as previously noted. The tank I16 is provided with an overflow passageway I18 so that the liquid flowing from the sump is maintained in the first tank for preliminary settling period before passing through the overflow I18 to tank I11. The liquid is drawn from tank I11 by a pump I19 mounted upon the wall of the chamber and driven by a V-belt I80 passing over a pulley I8I mounted upon the grit pump shaft. Pump I19 is a commercial product and therefore is not disclosed in detail. The liquid is drawn from the tank by the tube I82 and is conducted from the pump to the spray pipe by a tube I83 passing 'through the housing I24 with its end connected to the spraypipe.

Air blast nozzle In place of the grit blasting wheel, the grit may be blasted by air pressure, utilizing a nozzle by which high velocity air jets are introduced into the stream of liquid and grit discharged by the grit pump. As shown in Figure 12, the nozzle occupies approximately the same position as the mediate of its length to apply secondary air jets to the stream passing through the nozzle to raise 14 the velocity of the stream to its final blasting force.

Described in detail, the chamber I84 includes a plate I81 secured by screws I88 upon the flat side of the chamber, there being provided an opening I89 in the wall to permit entry of an air jet tube I90 which extends angularly into the chamber. To the outside of plate I81, there is secured an air intake nozzle I 9I to which is connected a supply tube I92 which conducts compressed air from a supply unit (not shown). The air blast passes through tube I90 which includes at its lower end a jet I93, directed toward the intake end of nozzle I 85. The stream of grit flows around the tube I90 in passing through chamber I84 and its velocity is increased by the introduction of air through the jet as the stream passes into the restricted opening formed by collar I94 which forms the discharge end of the chamber. The nozzle I85 is connected to the collar I94 by a coupling I95 screwthreaded upon the collar I94.

The nozzle I85 is oval as viewed in cross section and is flared downwardly to provide a diverging passageway so as to form a fan-shaped blast stream. In passing through the nozzle, the stream is further accelerated by the air chamber I86 which constitutes a housing preferably welded upon the outside of the nozzle to form an air manifold I96. The air is introduced into the manifold by a nipple I91 which is connected to a second compressed air supply line I 98. Air passes at high velocity into the moving stream by means of a series of jet apertures I99 drilled at an angle through the wall of the nozzle so as to direct the air jets into the stream at an angle to the direction of discharge. This arrangement provides substantially the same velocity and volumetric discharge of grit as provided by the grit blasting wheel.

The nozzle is mounted above the work table by means of a vertical shaft 200 having its lower end clamped in a socket 20I welded to one side of the transition chamber (Figure 12). The shaft is clamped in the socket by means of a set screw 202 threaded through the socket. Shaft 200 passes through the top wall of the treatment chamber and through a collar 203 welded to the underside of the wall. A set screw 204 is threaded into the collar to engage and lock the shaft and nozzle assembly in adjusted position with respect to the work table.

Having described my invention, I claim:

1. A method of grit blasting which comprises mechanically feeding grit particles to a pump at a controlled rate and therein forming a dynamic suspension of grit particles in liquid, moving the mixture of the grit particles and liquid at a low rate of velocity, and then imparting energy to the moving stream suflicient in amount to cause projection of the dynamic suspension at a high rate of velocity which is sufiicient to perform a grit blasting function.

2. The method of grit blasting with grit particles which are incapable of suspension in liquid in the absence of movement which comprises mechanically feeding grit particles and concurrently advancing liquid to a low velocity centrifugal pump, and thereby forming a dynamic suspension of the grit particles in the liquid in the form of a stream moving at low velocity, advancing the low velocity stream to a projector and therein accelerating the rate of movement of the stream to a high velocity effective for grit blasting, then collecting and recycling the components of the mixture to the pump.

3. An apparatus for Wet blasting work pieces with grit particles which are incapable of suspension in liquid in the absence of movement comprising; a chamber, a grit projector in the chamber adapted to propel a stream of grit and liquid against the work pieces at blasting velocity, the chamber being adapted to receive the grit particles and liquid discharged by the projector, conveyor means in the chamber adapted to feed grit particles from the chamber, at a controlled rate and a pump adapted to receive said grit particles andliquid from'the chamber and to propel the mixture to the projector at a velocity sufficient to maintain the grit particles in dynamic suspension in the liquid but insufficient to perform the blasting operation.

4. An apparatus for wet blasting work pieces with grit particles which are incapable of suspension in liquid in the absence of movement comprising; a chamber, a grit projector in the chamber adapted'to propel a stream of grit andliquid against the work pieces at blasting velocity, the chamber being adapted to receive the grit particles and iiquid discharged by the projector, conveyor means in the chamber adapted to feed grit particles from the chamber at a controlled rate, a separatory apparatus communicating with the chamber and arranged concurrently to separate suspended particles of dirt from the liquid, and a pump adapted to receive said grit particles and liquid from the chamber and to propel the mixture to the projector at a velocity sufiicient to said hopper at a controlled rate, and a pump adapted-to receive said grit particles and to mix the particles with carrier liquid drawn from the hopper and to propel the mixture to said grit projector at sufficient velocity to maintain the grit particles in dynamic suspension in the carrier liquid.

6. A wet grit blasting apparatus for the surface treatment of work pieces comprising; a chamber adapted to contain a supply of grit particles and liquid, a grit pump mounted adjacent the chamber, a screw conveyor mounted within the chamber and communicating with the grit pump,

a device associated with the screw conveyor arranged to feed the grit particles at a constant rate into the grit pump, means connected to the chamber above the level of grit particles and adapted to supply liquid from the chamber to the grit pump, a grit projector mounted within the chamber, and means connected to said pump to convey the liquid and grit to the projector at a velocity sufficient to maintain the particles in dynamic suspension in the liquid, the projector being arranged to accelerate the grit particles to a blasting velocity for impingement upon the work surfaces.

7. An apparatus for wet blasting work pieces with grit particles which are incapable of suspension in liquid in the absence of movement comprising; a reservoir adapted to contain a supply of grit particles and carrier liquid, a grit pump associated with the reservoir and adapted to intermin'gle the grit'particles and liquid and 16 to discharge themixture at sumcient velocity to maintain the grit particles in dynamic suspension, a grit projector for accelerating the mixture to blasting velocity, a conduit connecting the grit pump to the said grit projector for advancing the grit particles and liquid to the projector, means for advancing work pieces relative to the projector for impingement of the blast stream upon the work pieces, spray means adapted to project flushing liquid upon the work pieces, a pump for supplying liquid to the said spray means, said pump being. connected to the reservoir above the level of the grit particles to conduct the carrier liquid from the. reservoir for discharge to the said spray means.

8. An'apparatus for wet blasting work pieces with grit particles which are incapabl of suspension in liquid in the absence of .movement comprising; a reservoir adapted to contain a supplyof grit particles and carrier liquid, a grit pump associated with the reservoir and adapted to intermingle the grit particles and liquid and to discharge the mixture at sufficient velocity to maintain the grit particles in dynamic suspension, a grit projector for accelerating the mixture to blasting velocity, a, conduit connecting the grit pump to the said grit projector, means for advancing work pieces relative to the grit projector for impingement'of the blast stream upon' the work pieces, spray means adapted to project flushing liquid upon the work pieces after passage through the grit blast stream, a pump for supplying liquid to the said spray means, said pump being connected to the reservoir above the level of the grit particles to conduct the carrier liquid from the reservoir for discharge to the said spray means, and an apparatus for removing from the carrier liquid the foreign particles dislodged by the blast stream prior to the passage of the liquid to the spray means to provide a clear liquid for cleaning the work pieces.

9. A wet grit blasting apparatus comprising; a hopper adapted to contain a mass of grit particles and carrier liquid, a grit pump mounted adjacent the hopper and in communication therewith, a conveyor screw mounted within the lower e portion of the hopper and extending to the grit pump, the hopper having a grit discharge passageway communicating with the pump for passage of the grit particles advanced by the conveyor screw, a rotary controldisk having blades mounted upon the conveyor screw for rotation therewith, the disk being disposed within the discharge passageway, a stationary control disk secured within the said passageway adjacent the rotary control disk, said disks being adapted to control the passage of grit particles through the passageway to the grit pump, means for supplying carrier liquid to thepump, and a projector connected to the pump adaptedto accelerate the grit particles to blasting velocity.

10. A Wet grit blasting apparatus comprising; a chamber, a hopper in the lower portion of the chamber adapted to contain a mass of grit particles and carrier liquid, a grit projector adapted to propel a stream of grit and carrier liquid at blasting velocity, a grit pump mounted externally of the hopper, a conveyor screw rotatably mounted within the lower portion of the hopper, the hopper having a passageway communicating with the grit pump, said conveyor screw being extended through said passageway whereby the grit particles are fed by the screw conveyor to Tithe-grit pump in the presence of the carrier liquid, means for withdrawing carrier liquid from the hopper above the grit particles therein and conducting the same to the grit pump, and conduit means extending from the grit pump to the grit projector, the grit pump being adapted to mix the grit particles and carrier liquid and to propel the mixture to the grit projector at sufiicient velocity to maintain the grit particles in dynamic suspension in the carrier liquid.

11. A wet grit blasting apparatus comprising; a. chamber, a hopper in the chamber adapted to contain amass of grit particles and carrier liquid, a grit projector adapted to propel a stream of grit and carrier liquid at blasting velocity, a grit pump mounted externally of the hopper, a conveyor screw mounted within the lower portion of the hopper, the hopper having a passageway communicating with the grit pump, said conveyor screw being extended through said passageway whereby the grit particles are fed by the screw conveyor to the pump in the presence of the carrier liquid, a compartment externally of the hopper and extending upwardly from the pump, the compartment being adapted to maintain a carrier liquid level above the pump externally of the hopper at the level of the carrier liquid in the hopper, means for withdrawing carrier liquid from the hopper above the grit particles therein and conducting the same to the grit pump, and conduit means extending from the grit pump to the grit projector, the grit pump being adapted to mix the grit particles and carrier liquid and to propel the mixture to the grit projector at sufi'icient velocity to maintain the grit particles in dynamic suspension in the carrier liquid.

12. A wet grit blasting apparatus comprising;

within the lower portion of the hopper, the hopper having a passageway and said conveyor screw being extended through said passageway whereby the grit particles are fed by the screw conveyor to the opening in the top of the grit pump casing in the presence of the carrier liquid, a, compartment externally of the hopper extending upwardly from the top of the pump casing and adapted to maintain the carrier liquid above the pump casing at the level of the carrier liquid in the hopper, a drive shaft connected to the pump impeller and extending upwardly through said compartment, conduit means extending from the hopper to the bottom of the grit pump casing adapted to conduct carrier liquid from the hopper to the grit pump casing, and conduit means extending from the grit pump casing to the grit projector, the grit pump impeller being adapted to mix the grit particles and carrier liquid and to propel the mixture to the grit projector at sufficient velocity to maintain the grit particles in dynamic suspension in the carrier liquid.

NATHAN RANSOHOFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 705,347 Harris July 22, 1902 934,441 Hitchcock Sept. 21, 1909 1,321,528 Kann Nov. 11, 1919 1,849,557 Stelzer Mar. 15, 1932 1,966,571 Webb July 17, 1934 2,170,831 Minich Aug. 29, 1939 2,290,979 Luce July 28, 1942 2,317,837 Webster Apr. 27, 1943 2,369,576 Keefer Feb. 13, 1945 2,420,463 Cassin May 13, 1947 2,429,742 Barnes Oct. 28, 1947 2,462,480 Eppler Feb. 22, 1949 2,493,215 Barnes Jan. 3, 1950 

